Let’s understand what it means to be pro-life.
It is always wrong to intentionally kill an innocent human being.
Abortion is the intentional killing of an innocent human being prior to birth.
Therefore, abortion is always wrong.
Legal Addendum: Therefore, abortion should be illegal.
In short, killing human beings inside the womb should be illegal for all the same reasons killing a human being outside the womb is illegal.
The entity in the womb is not a human being.
It is okay to kill innocent human beings (at least sometimes).
Outlawing abortion does more harm than good.
The definition of morality is up for debate.

Let’s understand what it means to be pro-life.
It is always wrong to intentionally kill an innocent human being.
Abortion is the intentional killing of an innocent human being prior to birth.
Therefore, abortion is always wrong.
Legal Addendum: Therefore, abortion should be illegal.
In short, killing human beings inside the womb should be illegal for all the same reasons killing a human being outside the womb is illegal.
The entity in the womb is not a human being.
It is okay to kill innocent human beings (at least sometimes).
Outlawing abortion does more harm than good.
The definition of morality is up for debate.
